NiceGUI is vulnerable to XSS via Unescaped URL in ui.navigate.history.push() / replace()

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2026-21871: 0.27% estimated exploitation activity in the next 30 days; percentile 19.77 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary XSS risk exists in NiceGUI when developers pass attacker-controlled strings into ui.navigate.history.push() or ui.navigate.history.replace(). These helpers are documented as History API wrappers for updating the browser URL without page reload. However, if the URL argument is embedded into generated JavaScript without proper escaping, a crafted payload can break out of the intended string context and execute arbitrary JavaScript in the victim’s browser. Applications that do not pass untrusted input into ui.navigate.history.push/replace are not affected. Details NiceGUI provides ui.navigate.history.push(url) and ui.navigate.history.replace(url) to update the URL using the browser History API. If an application forwards user-controlled data (e.g., URL path segments, query parameters like next=..., form values, etc.) into these methods, an attacker can inject characters such as quotes and statement terminators to escape the JavaScript string context and execute arbitrary code. A…

Published by the source

8 Jan 2026, 20:00 UTC

Last modified by the source

7 Jul 2026, 17:57 UTC

Source last checked

26 Oct 2026, 13:36 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-7grm-h62g-5m97

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-7grm-h62g-5m97

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# Patch Next advisory brief: CVE-2026-21871

Advisory: NiceGUI is vulnerable to XSS via Unescaped URL in ui.navigate.history.push() / replace()
IDs: CVE-2026-21871, GHSA-7grm-h62g-5m97
Record: https://patchnext.com/advisories/cve-2026-21871 (revision 2, source checked 26 Oct 2026, 13:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nicegui 3.5.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI nicegui: affected >= 2.13.0, <= 3.4.1; fixed in 3.5.0

## Suggested inspection (read-only)
- `python -m pip show nicegui`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nicegui.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-7grm-h62g-5m97 (OSV record GHSA-7grm-h62g-5m97 lists affected ranges: PyPI nicegui >=2.13.0 <3.5.0 (fixed))
- Verified: https://github.com/advisories/GHSA-7grm-h62g-5m97 (GitHub-reviewed advisory GHSA-7grm-h62g-5m97 lists affected ranges: PyPI nicegui >=2.13.0 <=3.4.1)

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